1. Field of the Invention
In general, this invention relates to an embossed multilayer film and, more particularly, to a film comprising an embossed base layer and an overlying, conformable, protective surface layer.
2. Description of the Related Art
On site application of paint directly to a surface to be decorated is a time-honored method for providing decorative and functional graphic designs. While this approach provides many desirable aesthetic and physical features including realistic appearance, color flexibility, and durability to abrasion, weather and chemical degradation, it suffers from many disadvantages. Such disadvantages include the need for relatively skilled labor, long application times, and potential contamination to adjacent areas and mechanical equipment.
As a result, various prefabricated graphics have been developed. A typical prefabricated graphic comprises a plastic base film having an adhesive on one surface and, optionally, a design or decoration on the opposite surface. The design or decoration may comprise one or more color layers that provide a mono- or polychromatic appearance. In other instances, the design may be an embossed pattern that imparts a pebbled, sandblasted, simulated leather or other desirable finish to the plastic film. Combinations of color and embossing may also be used.
Some plastic films conventionally used in graphic designs do not possess sufficiently inherent resistance to the effects of environmental weathering, chemical exposure or abrasion to permit use in outdoor settings without being supplemented by a protective surface layer. Unfortunately, however, the use of protective surface layers in combination with an underlying embossed plastic film has, heretofore, presented difficult problems, solutions to which have long been sought. For example, many protective surface layers comprise relatively rigid and brittle thermoset polymers that are not readily embossed or sufficiently flexible, certain acrylic based materials being particularly notable in this regard. In such constructions, it is not facile to apply the surface layer to the plastic base film and subsequently emboss the multilayer construction.
One possible solution is to apply the surface layer after the plastic base film has been embossed. However, if it is necessary to use heat during application of the surface layer, the embossed pattern may lose some of its sharpness and distinctiveness. In more severe cases, the underlying base film may soften or even melt causing a catastrophic deterioration of the embossed pattern.
While it may be possible to spray the surface layer material onto the embossed base film, this may result in a surface layer of uneven thickness. Depressed areas of the emboss tend to accumulate more surface layer material than elevated flat ridges. Angular transition surfaces between the ridges and the depressions may accumulate more or less surface layer material depending on their profile. A surface layer of variable thickness can detrimentally affect the ability of the underlying base film to resist weathering, chemical exposure and abrasion. Also, low gloss surface layers may display a noticeable variation in gloss if the surface layer is not uniformly thick. Finally, uneven surface layers tend to soften or blur the sharpness of the embossed pattern.
U.S. Pat. No. 4,214,028, "Resinous Polymer Sheet Materials Having Surface Decorative Effects and Methods of Making the Same," issued July 22, 1980 to H. A. Shortway et al. discloses sheet materials that comprise a substrate such as a fibrous backing sheet and/or a blown or unblown resinous sheet polymer. A design is printed on the substrate and portions of the printed design contain a polymerization initiator. The sheet material further includes a wear layer containing reactive polymerizable monomers dispersed or dissolved in a poly(vinyl chloride) resin. The sheet is embossed at a sufficiently elevated temperature to cause the reactive polymerizable monomers overlying the portions of the printed design that contain the polymerization initiator to polymerize and crosslink, this occurring primarily during the embossing process. Reportedly, if crosslinking of the polymerizable reactive monomer takes place too early in the over-all procedure, then the desired embossment may be difficult or even impossible to obtain. It is also stated that if crosslinking of the polymerizable reactive monomer takes place too late, then, perhaps, it may be too late for certain embossed areas of the wear layer to retain their embossment.
Poly(vinyl chloride) (PVC) is a widely used film in the graphics industry. It can be embossed, pigmented or have a color layer screen printed thereon. PVC films are often associated with the use of organic solvents or plasticizers. However, for various health and environmental reasons, it is desirable to reduce or eliminate the use of solvents and plasticizers as well as PVC itself.
Consequently, there is considerable need for a durable embossed graphic that is substantially free of PVC.